U.S. patent number 10,541,589 [Application Number 15/738,259] was granted by the patent office on 2020-01-21 for motor vehicle starter equipped with a thermal protection system.
This patent grant is currently assigned to Valeo Equipements Electriques Moteur. The grantee listed for this patent is Valeo Equipements Electriques Moteur. Invention is credited to Jeremie Chamroux, Thierry Paltrie.
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United States Patent |
10,541,589 |
Paltrie , et al. |
January 21, 2020 |
Motor vehicle starter equipped with a thermal protection system
Abstract
The invention relates mainly to a starter for a heat engine of a
motor vehicle comprising: at least one electromagnetic switch
comprising a positive output terminal, at least one electric motor,
said electric motor comprising: a stator comprising coils, each of
the coils being wound around a pole piece to form a pole, at least
one brush cage (43), at least one positive brush (35) mounted in
said brush cage, an electrical path between said positive brush
(35) and the positive output terminal (32), and at least one
thermal protection (96) located in said electrical path, in which
said thermal protection is able to disconnect said two elements
(93, 95) when the thermal protection has a temperature above a
temperature threshold for electrically disconnecting said positive
output terminal with respect to said positive brush (35).
Inventors: |
Paltrie; Thierry (Isle D'abeau,
FR), Chamroux; Jeremie (Isle D'abeau, FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Valeo Equipements Electriques Moteur |
Creteil |
N/A |
FR |
|
|
Assignee: |
Valeo Equipements Electriques
Moteur (Creteil, FR)
|
Family
ID: |
55236439 |
Appl.
No.: |
15/738,259 |
Filed: |
June 22, 2016 |
PCT
Filed: |
June 22, 2016 |
PCT No.: |
PCT/FR2016/051528 |
371(c)(1),(2),(4) Date: |
May 16, 2018 |
PCT
Pub. No.: |
WO2016/207547 |
PCT
Pub. Date: |
December 29, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180248452 A1 |
Aug 30, 2018 |
|
Foreign Application Priority Data
|
|
|
|
|
Jun 26, 2015 [FR] |
|
|
15 55913 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02H
7/0852 (20130101); H02K 11/25 (20160101); F02N
11/10 (20130101); H02K 5/148 (20130101); H02K
1/14 (20130101); H02H 7/0822 (20130101); F02N
11/0814 (20130101) |
Current International
Class: |
H02K
11/25 (20160101); H02K 5/14 (20060101); H02H
7/08 (20060101); H02K 1/14 (20060101); F02N
11/10 (20060101); H02H 7/085 (20060101); F02N
11/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
19911070 |
|
Sep 2000 |
|
DE |
|
2373905 |
|
Jul 1978 |
|
FR |
|
2717961 |
|
Sep 1995 |
|
FR |
|
2949626 |
|
Mar 2011 |
|
FR |
|
2978500 |
|
Mar 2015 |
|
FR |
|
3016754 |
|
Jul 2015 |
|
FR |
|
Other References
International Search Report issued in corresponding application No.
PCT/FR2016/051528 dated Sep. 6, 2016 (6 pages). cited by applicant
.
Written Opinion of the International Searching Authority issued in
corresponding application No. PCT/FR2016/051528 dated Sep. 6, 2016
(6 pages). cited by applicant .
International Preliminary Report on Patentability from
PCT/FR2016/051528 completed on Dec. 26, 2017 (14 pages). cited by
applicant.
|
Primary Examiner: Desai; Naishadh N
Attorney, Agent or Firm: Osha Liang LLP
Claims
The invention claimed is:
1. A starter for a heat engine of a motor vehicle comprising: at
least one electromagnetic switch comprising a positive output
terminal; and at least one electric motor, said electric motor
comprising: a stator comprising coils, each of the coils being
wound around a pole piece to form a pole, at least one brush cage,
at least one positive brush mounted in said brush cage, an
electrical path between said positive brush and the positive output
terminal, and at least one thermal protection located in said
electrical path, wherein said thermal protection is configured to
disconnect two of a plurality of elements when the thermal
protection has a temperature above a temperature threshold for
electrically disconnecting said positive output terminal with
respect to said positive brush, and wherein at least one other of
the plurality of elements of said electrical path is a fuse
configured to melt above a predetermined current, wherein said
thermal protection and said fuse are two separate elements.
2. The starter according to claim 1, wherein said temperature
threshold corresponds to an abnormal condition of the starter
causing heating that could damage the vehicle.
3. The starter according to claim 1, wherein said thermal
protection is arranged in said electric motor so that a main factor
allowing the temperature threshold to be reached in case of an
abnormal condition is transmission of heat corresponding to an
abnormal operating condition to said thermal protection, by heat
conduction and/or by convection.
4. The starter according to claim 1, wherein, in case of
short-circuit, said fuse is able to act by melting and electrically
disconnect said positive output terminal with respect to said
positive brush.
5. The starter according to claim 1, wherein said fuse consists of
a braid of the positive brush.
6. The starter according to claim 1, wherein said fuse is located
in the electrical path between the thermal protection and a coil
connecting bridge.
7. The starter according to claim 1, in wherein which said thermal
protection comprises a solder with a low melting point joining
together a first element and a second element of said electrical
path, said solder being able to melt above said temperature
threshold, wherein, in an operating state of the starter, the
solder is able to be in a solid state to connect the first element
to the second element, and in case of an abnormal condition on the
starter, said solder is able to pass into the molten state to allow
said thermal protection to separate said two elements of the
electrical path.
8. The starter according to claim 7, wherein said thermal
protection comprises a stop that is able to retain one of the two
elements of said electrical path following fusion of the
solder.
9. The starter according to claim 7, wherein said thermal
protection comprises a guiding device of the movement of one of the
two elements of said electrical path following fusion of the
solder.
10. The starter according to claim 9, wherein said conductor
consists of an elongated stud passing through a grommet mounted on
said frame.
11. The starter according to claim 8, wherein said electrical
protection comprises an elastic element able to exert a pressure on
one of the elements of said electrical path joined together by said
solder, wherein said elastic element, said stop, and said guiding
device are integral with said grommet.
12. The starter according to claim 8, wherein one of the elements
of said electrical path is a conductor and another element of said
electrical path is a connector joining said conductor electrically
to at least one coil, these two elements being joined together by
said solder, and wherein said connector is in the form of a
hook.
13. The starter according to claim 5, wherein said hook 15
comprises a portion of a ring partly surrounding the conductor and
a tab for connecting electrically to said coils.
14. The starter according to claim 8, wherein one of the elements
of said electrical path is a conductor and another element of said
electrical path is a connector joining said conductor electrically
to at least one coil, these two elements being joined together by
said solder, and wherein said connector is connected to the coils
via a connecting bridge, called coil bridge, soldered to at least
one coil.
15. The starter according to claim 14, wherein said coil bridge is
mounted electrically between said connector and said coils.
Description
The present invention relates to a motor vehicle starter equipped
with a thermal protection system. The invention may be applied
particularly advantageously, but not exclusively, with the starters
of systems for automatic stop and start of heat engines.
In a manner known per se, starters comprise means for overcurrent
protection, taking the form of one or more fuses and/or one or more
circuit breakers. Thus, FIG. 1 shows an example of a starter motor
1 comprising a fuse 2 mounted in series between a supply terminal 3
of the electrical machine 1 and windings 4.1-4.4 of the stator of
said motor.
The fuse is intended to melt to cut the electrical supply to the
motor when a predetermined maximum current passes through it. This
makes it possible to prevent damage to the starter or its
surroundings owing to the heat produced by an excess current. An
excess current notably appears when rotation of the motor's rotor
is blocked.
In no-load or low-load operation of the machine (i.e. operation
between about 0 and 25% of the nominal load), the no-load rotary
speed of the rotor also leads to heating of the electrical machine,
which may damage the starter over time. This heating, notably due
to mechanical friction between the brushes 6.1-6.4 and the
commutator, arises for example at overspeed when the starter pinion
driven by the heat engine turns more quickly than the shaft driven
by the starter's rotor. However, in this case, the current passing
through the fuse may be too low to cause melting of the fuse 2,
even over a long period.
Document FR140573 filed on 23 January by Valeo describes a compact
thermal protection system 5 for cutting the electrical supply to
the motor in both the aforementioned cases (in the case of blocking
and in the case of operation at low load). More precisely, this
system is configured so that in case of overheating, a part
overmoulded on the plate of the brush holder deforms, in such a way
that the brush cages of positive polarity that are subject to the
action of springs come into contact with the plate connected to the
terminal with negative polarity. A short-circuit is thus created,
causing opening of the starter's fuse.
The invention aims to improve the thermal protection of the starter
in the case of a low level of charge of the vehicle's battery that
may make opening of the fuse difficult, even in the case of
short-circuit.
For this purpose, the invention proposes a starter for a heat
engine of a motor vehicle comprising: at least one electromagnetic
switch comprising a positive output terminal, at least one electric
motor, said electric motor comprising: a stator comprising coils,
each of the coils being wound around a pole piece to form a pole,
at least one brush cage, at least one positive brush mounted in
said brush cage, an electrical path between said positive brush and
the positive output terminal, and at least one thermal protection
located in said electrical path, in which said thermal protection
is able to disconnect two elements when the thermal protection has
a temperature above a temperature threshold for electrically
disconnecting said positive output terminal with respect to said
positive brush.
The invention thus makes it possible to cut the supply circuit to
the electric motor in a manner that mainly depends on the
temperature level in the starter. This thus ensures cutting of the
supply circuit regardless of the level of charge of the vehicle's
battery.
According to one embodiment, said temperature threshold corresponds
to an abnormal condition of the starter causing heating that could
damage the vehicle.
According to one embodiment, said thermal protection is arranged in
said electric motor in such a way that a main factor allowing the
temperature threshold to be reached in case of an abnormal
condition is transmission by heat conduction and/or by convection
of heat corresponding to an abnormal condition to said thermal
protection.
According to one embodiment, at least one other of the elements of
said electrical path is a fuse that is able to melt above a
predetermined current, said thermal protection and said fuse being
two separate elements.
According to one embodiment, in case of short-circuit, said fuse is
able to act by melting for electrically disconnecting said positive
output terminal with respect to said positive brush.
According to one embodiment, said fuse consists of a positive brush
strap.
According to one embodiment, said fuse is located in the electrical
path between the thermal protection and a coil connecting
bridge.
According to one embodiment, said thermal protection comprises a
low melting point solder joining together a first element and a
second element of said electrical path, said solder being able to
melt above said temperature threshold, in which, in an operating
state of the starter, the solder can be in a solid state to connect
the first element to the second element, and in the case of an
abnormal condition of the starter, said solder can enter the molten
state to allow said thermal protection to separate said two
elements of the electrical path.
According to one embodiment, one of the elements of said electrical
path is a conductor and another element of said electrical path is
a connector joining said conductor electrically to at least one
coil, these two elements being joined together by said solder.
According to one embodiment, said electrical protection comprises
an elastic element that is able to exert pressure on one of the
elements of said electrical path joined together by said solder.
This thus facilitates disconnection of the two elements in case of
overheating.
According to one embodiment, said thermal protection comprises a
stop that is able to retain one of the two elements of said
electrical path following fusion of the solder. The positioning of
the moving free element is thus controlled following fusion of the
solder.
According to one embodiment, said thermal protection comprises a
device for guiding the movement of one of the two elements of said
electrical path following fusion of the solder.
According to one embodiment, said conductor consists of an
elongated stud passing through a grommet mounted on said frame.
According to one embodiment, said elastic element, said stop, and
said guiding device are integral with said grommet.
According to one embodiment, said connector is in the form of a
hook.
According to one embodiment, said hook comprises a portion of a
ring partly surrounding the conductor and a tab for electrical
connection to said coils.
According to one embodiment, said connector is connected to the
coils by means of a connecting bridge, called coil bridge, soldered
to at least one coil.
According to one embodiment, said coil bridge is mounted
electrically between said connector and said coils.
According to one embodiment, positive brush braids are soldered to
said coil bridge.
According to one embodiment, a second connecting bridge is soldered
to an output of at least one coil and soldered to positive brush
braids.
According to one embodiment, a fuse is mounted between said
connector and said coil bridge.
According to one embodiment, an insulating layer arranged for
electrically insulating said brush cage relative to a supporting
plate is deformable starting from another temperature threshold,
and an elastic means pressing said positive brush against a contact
plate of a commutator is able to establish contact between said
brush cage and said supporting plate following deformation of said
deformable insulating layer.
The invention will be better understood on reading the description
given hereunder and on examining the accompanying figures. These
figures are only given for purposes of illustration and do not
limit the invention in any way.
FIG. 1, already described, shows a schematic diagram of an electric
motor of a motor vehicle starter equipped with a thermal protection
system;
FIG. 2 is a longitudinal sectional view of a starter of a motor
vehicle heat engine according to the present invention;
FIG. 3 shows a perspective view of a brush holder belonging to the
starter in FIG. 2,
FIG. 4 is a detailed perspective view of an embodiment example of
the thermal protection employed in the motor vehicle starter
according to the present invention;
FIGS. 5a and 5b are circuit diagrams illustrating variants of
connection of the coils of the stator belonging to the electric
motor of the starter according to the present invention;
FIG. 6 is a perspective representation of the supporting plate of
the brush holder in FIG. 3;
FIG. 7 is a graph showing the variation, as a function of time, of
the temperature of the starter, of the supply voltage of the
starter, and of the current circulating in the commutator during
activation of the thermal protection.
Elements that are identical, similar, or analogous keep the same
reference from one figure to another.
Referring to FIG. 2, the starter 11 according to the invention
notably comprises a drive shaft 12, a starter 13 mounted on the
drive shaft 12, and an electric motor 15 consisting of an inducing
stator 16 and an induced rotor 17 integral with a shaft 18. The
motor 15 comprises a frame 21 mounted on a support 22 of the
starter 11 intended to be fixed on a fixed part of the motor
vehicle.
A speed reducer 23 with gears of the epicycloid type is preferably
inserted between a rear end of the drive shaft 12 and the shaft 18
of the electric motor 15.
The starter 11 also comprises an electromagnetic switch 25
extending parallel to the electric motor 15, being installed
radially above the latter. The switch 25 has a metal casing 28
equipped with a set of exciting coils 29a, 29b. Terminals 31, 32
are configured so that they each form a fixed contact inside the
casing 28. One of the terminals 31 is intended to be connected to
the positive terminal of the vehicle's battery. The other terminal
32, called positive output terminal, is connected to the input of
the inducing winding of the stator 16 and to the brushes 35 with
positive polarities, as is explained in more detail hereunder.
These brushes 35 rub on conductive plates 38 of a commutator 39 to
supply the rotor winding. The brushes 35 belong to a brush holder
42 equipped with cages 43 to guide and receive the brushes 35.
These brushes 35 are pressed towards the conductive plates 38 by
elastic means 44 of the spring type. A bearing 45 of the rear
flange serves for rotatable mounting of one end of the shaft 18 of
the electric motor 15.
In a known manner, on excitation of the pull-in coil 29a, a moving
core 48 is drawn by magnetic attraction towards a fixed core 49 of
the switch 25, to act on the one hand, after compensating any play,
on a rod 50 bearing a moving contact 51 to cause closure of the
contacts 31, 32 of the switch 25 and supply the electric motor 15,
and on the other hand to actuate a control lever 52 acting on the
starter 13. The upper end of the lever 52 is mounted in a known
manner, hinged on a moving rod 55 connected elastically to the
moving core 48 via a spring 56, called a tooth-against-tooth
spring, housed in the moving core 48.
The starter 13 may thus pass from a position of rest in which a
drive pinion 60 is located at a distance from the starter ring gear
of the heat engine to an active position in which the drive pinion
60 interacts with the starter ring gear of the heat engine. The
drive shaft 12 then transmits torque from the electric motor 15 to
the drive pinion 60 by means of a pinion body 61, via a
free-wheeling mechanism 62. Following deactivation of switch 25,
the starter 13 returns from its active position to its position of
rest.
When the starter 13 is in an active position, the pinion body 61 is
driven, via the free-wheeling mechanism 62, by a driver 65. For
this purpose, the pinion body 61 is mounted on the drive shaft by
means of two pads 68, 69 of annular shape.
The pinion body 61 is mounted rotatably in a front bearing 70 of
the support 22. As an example, this bearing 70 consists of a ball
bearing or, as a variant, a needle bearing, or a plain bearing.
The free-wheeling mechanism 62 is, for example, of the type with
rollers, but could as a variant be replaced by a cone clutch device
or a clutch equipped with several friction disks, as described in
document FR2978500.
In a known manner, the driver 65 is provided internally with
helicoidal splines engaging in complementary fashion with external
helicoidal teeth on the drive shaft 12. Thus, a helicoidal movement
is imparted to the starter 13 when it is displaced by the lever 52
to come into the active position, by means of the pinion 60, in
engagement with the starter ring gear of the heat engine.
The drive pinion 60 being connected in rotation and mounted sliding
axially relative to the pinion body 61 by means of sets of grooves
of complementary shape, a spring 71 presses the drive pinion 60
towards an axial stop 72 formed for example by a circlip. The
spring 71 will be compressed in such a way that the pinion 60 moves
back in case of impact of the pinion 60 with the starter ring
gear.
FIG. 3 is a detailed view of the brush holder 42 with axis X
comprising a supporting plate 75 of roughly annular shape on which
the set of cages 43 is fixed, each serving as a housing for a brush
35. As can clearly be seen in FIG. 6, the supporting plate 75 is of
a single piece comprising a metal plate 76 and overmoulded layers
77 provided on either side of the metal plate 76. The overmoulded
layers 77 are made of plastic for good electrical insulation. The
overmoulded layers 77 protect, at least partly, the brush
supporting face as well as the opposite face. The overmoulded
layers 77 are sensitive to heat and are deformable starting from a
temperature threshold T1. The temperature threshold T1 corresponds
to a temperature above which the starter 11 and/or its surroundings
would possibly be damaged.
Various plastics are usable depending on the applications and the
stresses to which they are subjected. Typically, the plastic used
for the overmoulded layers 77 is a thermoplastic such as a
polyamide PA4.6 or PA6.6 or a polypropylene PPS filled with glass
fibres to between 40 and 50%. Thermosetting plastics may also be
envisaged. The metal plate 76 is typically obtained by stamping
from a free-machining steel, for example FePO5.
The supporting plate 75 and the cages 43 that it carries will be
fixed on the flange forming the rear bearing 45 for the shaft 18 of
the electric motor 15. Furthermore, the central part of plate 75
comprises an opening 78 by which the assembly that it forms with
the cages 43 and the brushes 35 is mounted around the shaft 18 of
the electric motor 15.
Each brush 35 is mounted with sliding motion inside a cage 43,
which is open on the side of the axis X to allow electrical contact
of the brushes 35 with the plates 38 of the commutator 39. More
precisely, each cage 43 is made by folding a thin plate of sheet
metal, the end branches of which are fixed on the plate 75. One of
the side walls has a notch 81, visible in FIG. 3, to allow passage
of the arm of the corresponding spring 44. From the outer face of
the commutator 39, each cage 43 may comprise flaps 85 extending on
either side of the brush 35 to prevent dust generated by the
friction of the brushes 35 with the plates 38 affecting the
operation of the brush holder 42.
Each cage 43 further comprises a system for fixing to the plate 75.
Each fixing system is formed for example by tabs 86 interacting
with the openings 88 made in the plate 75. Alternatively, the cages
43 are fixed on the plate 75 by means of rivets.
Moreover, a spiral spring 44 associated with each cage 43 presses
the corresponding brush 35 radially towards the contact plates 38
of the commutator 39. Each spring 44 comprises a wound part formed
by a plurality of turns, as well as an arm intended to bear against
the rear face of the corresponding brush 35. Each spring 44 is in
this case mounted around a holding system 87 formed by a pin
extending axially relative to the axis X.
The brushes 35 of positive polarity are connected electrically to
the positive output terminal 32 of the switch 25 via an electrical
path 91. This electrical path 91 is thus formed by the set of
elements conducting the current between the output terminal 32 and
the brushes 35 of positive polarity. As can be seen in FIG. 3, this
electrical path 91 is notably formed by the following elements: a
first conductor 92 providing electrical connection between the
positive output terminal 32 of the switch 25 and a second conductor
93, said second conductor 93 consisting of a rigid elongated stud
passing through a grommet 94 interacting with the frame 21 for
hermetically isolating the brush holder 42 with respect to the
external environment, and a connector 95
having a hook shape. As is more easily seen in FIG. 4, the
connector 95 comprises a ring portion 951 partly surrounding the
stud 93 and a tab 952 to be connected electrically to coils 111
belonging to the stator 16 of the electric motor 15. These coils
111 are each mounted around a pole piece to form a pole.
Thus, in the embodiment in FIG. 5a, two sets E1, E2 of coils 111
are mounted in parallel, each set E1, E2 comprising two coils 111
mounted electrically in series. The first ends of the two sets E1,
E2 are soldered to a first connecting bridge 113, called a coil
bridge, to which the tab 952 is also connected electrically. The
second ends of the two sets E1, E2 are soldered to a second
connecting bridge 114. The braids of the positive brushes 35 are
also soldered to the connecting bridge 114.
As a variant, all the coils 111 are connected in parallel with one
another between the two bridges 113, 114, as in the embodiment in
FIG. 1.
In the embodiment in FIG. 5b, two sets E1, E2 of coils 111 are
mounted in parallel, each set E1, E2 comprising two coils 111
mounted electrically in series. The first ends of the two sets E1,
E2 as well as the braids of the positive brushes 35 are soldered to
the coil bridge 113, to which the tab 952 is also connected
electrically. The second ends of the two sets E1, E2 of coils are
connected electrically to earth.
Furthermore, one of the elements located in the electrical path 91
is a fuse that is able to melt above a predetermined current, for
example of the order of 100 A. Thus, in case of a short-circuit
generating such a current, the fuse acts by melting for
electrically disconnecting the positive output terminal 32 with
respect to the positive brush 35. In this case, a fuse 116 is used,
mounted between the connector 95 and the coil bridge 113 employed
in the embodiment in FIGS. 5a and 5b. Alternatively or
additionally, two fuses are used, each consisting of a flexible
braid 82 of positive brush 35 made of copper or copper alloy. As a
variant, it would be possible to use dedicated fuses inserted in
the electrical path 91.
Moreover, a thermal protection 96 separate from the fuse is located
in the electrical path 91. In this case, as can be seen in FIGS. 3
and 4, the thermal protection 96 comprises a solder 97 with a low
melting point connecting the connector 95 to the stud 93, via the
portion 951.
The solder 97 is thus able to melt above a temperature threshold T2
corresponding to an abnormal condition of the starter causing
heating that could damage the vehicle. This temperature threshold
T2 is below 300.degree. C. and for example between 230.degree. C.
and 260.degree. C. The solder 97 is preferably formed from an alloy
of copper and tin, the level of copper being below 10%. The level
of copper is for example of the order of 2%.
The thermal protection 96 is arranged in the electric motor 15 in
such a way that a main factor allowing the temperature threshold T2
to be reached in the case of an abnormal condition is transmission
by heat conduction and/or by convection of heat corresponding to
the abnormal condition to the thermal protection 96, and not a
current passing through the thermal protection 96. This heat may
for example be generated notably by dust due to wear of the brushes
35, a malfunction of a mechanical component, or an electrical
malfunction of the starter.
The thermal protection 96 is in this case located near the rear
bearing inside the interior space delimited by the frame 21. As a
variant, the positioning may be adapted so that the thermal
protection can be located outside the frame 21. In all cases, the
thermal protection 96 is positioned near the elements that are
likely to generate considerable heat in the case of an abnormal
condition for transmission by convection and/or by conduction to
the thermal protection 96.
Furthermore, it should be noted that the solder of the thermal
protection 96 does not necessarily have the highest electrical
resistance of the elements of the electrical path 91. Preferably,
the thermal protection 96 even has a low electrical resistance so
that the current contributes to its heating as little as
possible.
Furthermore, in certain cases, the melting point of the solder 96
may be lower than all the melting points of the various elements of
the electrical path 91.
However, in other cases, the melting point of the solder 96 is
above the melting point of the fuse, in this case consisting of one
or more braids 82. However, owing to the aforementioned arrangement
of the thermal protection 96, the thermal protection 96 may have a
higher temperature than the fuse in the case of an abnormal
operating condition, which causes the thermal protection 96 to melt
before the fuse.
Preferably, the thermal protection 96 further comprises an elastic
element 98 pretensioned axially between the brush holder 42 (here
the plate 75 of the brush holder 42) and the connector 95. This
elastic element 98 is able to exert an axial pressure on the
connector 95. In this case, the elastic element 98 consists of at
least one stud forming a single piece with the grommet 94
pretensioned radially relative to the axis X' of the stud 93
between the grommet and the tab 952 of the connector 95. When the
solder 97 is in the solid state, it connects the connector 95 to
the stud 93, and allows the connector 95 to withstand the axial
force applied by the pretensioned elastic element 98. However, when
the solder 97 then enters the molten state, the connector 95, which
is no longer retained by the solder 97, is moved away from the stud
93 owing to the force exerted by the elastic element 98.
As can be seen in FIG. 4, the thermal protection 96 preferably
comprises a stop 101 that is able to retain the connector 95
following fusion of the solder 97. The final positioning of the
connector 95 after its displacement caused by the elastic element
98 is thus controlled. In the embodiment in FIG. 4, the stop 101
has the form of a portion of a ring located opposite the portion
951.
The thermal protection 96 further comprises a guiding device 103 of
the displacement of the connector 95 following fusion of the
solder. This guiding device 103 is formed by two guides 104 located
on either side of the stud 93, providing radial guidance relative
to the axis X' of the connector 95 towards the stop 101. These
guides 104 also provide axial guidance relative to axis X' of the
stud 93 to prevent the connector 95 falling into the brush holder
42, which could cause short-circuit problems.
Moreover, the brushes 35 of negative polarity intended for current
return are connected electrically to the frame of the machine by
means of their respective braid 82 welded on the plate 76. The
brushes 35 of positive polarity and their corresponding cage 43 are
insulated electrically from the negative polarity for proper
operation of the starter 11. This insulation is provided by the
overmoulded layers 77.
Activation of the thermal protection 96 in the case of malfunction
of the starter 11 is described below.
In the case of a short-circuit occurring in the electric motor of
the starter while the vehicle's battery has a high level of charge,
the fuse 116 and/or the two braids 82 of brushes forming a fuse
will melt one after the other. In fact, owing to their different
resistances (it is in fact impossible to produce braids 82 having
exactly identical resistances), one of the braids 82 melts before
the other in the case of a short-circuit. When one of the braids
has melted, the other will melt immediately thereafter because of
the considerable increase in current passing through the brushes 35
to which the second braid is connected.
In the case when the level of charge of the vehicle's battery is
high and a malfunction occurs that does not necessarily generate a
short-circuit, such as notably overheating caused for example by
no-load operation of the starter 11 for a long time, the
temperature threshold T1 is reached. The insulating layers 77
overmoulded on the plate 75 then deform, so that the force exerted
by the spring 44 on the holding system 87 causes swivelling of the
cages 43 of positive polarity, which then come into contact with
the metal plate 76 to establish a short-circuit. This short-circuit
causes a considerable increase in the current passing through the
machine, which has the effect of causing the braids 82 to melt,
thus cutting the supply to the electric motor.
In the case illustrated in FIG. 7, where the level of charge of the
vehicle's battery is low and overheating occurs, caused for example
by no-load operation of the starter 11 for a long time, the
temperature rises in the starter whereas the current does not reach
the threshold current (here 100 A) allowing fusion of the braids of
the positive brushes forming a fuse. Then, when the temperature
reaches the melting point of the solder 97, which is in this case
slightly above 250 degrees Celsius, the connector 95, which is no
longer retained by the solder 97, is moved away from the stud 93
owing to the force exerted by the elastic element 98. This has the
effect of disconnecting the output terminal 32 electrically with
respect to the brushes of positive polarity 35. The starter 11 then
passes from the operational state to a non-operational state of the
starter 11 in which the motor 15 is no longer supplied because the
electrical path 91 has been cut. Note that during its displacement,
the connector 95 is guided by the guiding device 103 towards the
stop 101, which then stops its displacement to prevent the latter
causing short-circuits.
We thus have two systems for thermal protection of the starter 11,
which will be able to act in different operating conditions of the
starter. As a variant, it would be possible to dispense with the
thermal protection system based on the use of the overmoulded plate
generating the short-circuit, using only the thermal protection 96
with the fuse 116 and/or the fuses formed here by the braids 82 of
the positive brushes.
A person skilled in the art will of course be able to modify the
configuration of the brush holder 42 described above, while
remaining within the scope of the invention.
Thus, as a variant, the thermal protection 96 is located between
two other elements of the electrical path 91, for example between
the first conductor 92 and the second conductor 93.
As a variant, the electrical path 91 does not have a second
conductor 93, the first conductor 92 passing inside the grommet 94
and being connected directly to the connector 95.
As a variant, the elastic element 98 exerts a radial force on the
connector 95, being pretensioned radially relative to the axis X
for example between the connector 95 and the frame 21.
As a variant, the thermal protection 96 lacks an elastic element
98, separation of the two elements 93, 95 following fusion of the
solder 97 being effected solely by gravity.
Alternatively, the plate 75 is connected electrically to the
positive polarity. The spiral spring 44 may also be replaced with a
cylindrical spring supported by the cover to push the corresponding
brush 35 against the plates 38 of the commutator 39.
As a variant, the brush holder 42 comprises more than four brushes
35, and each brush 35 may for example be associated with another
brush 35 positioned on the side opposite the plate 75.
The brush holder 42 is in this case a machine brush holder of a
motor vehicle starter. As a variant, the brush holder could also
belong to an alternator or to an alternator-starter.
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